The present invention relates to a process for producing, from xcex1-aminodihalomethyl ketone derivatives, the corresponding xcex1-aminohalomethyl ketone derivatives; a process for producing the corresponding xcex2-aminoalcohol derivatives by reducing the xcex1-aminohalomethyl ketone derivatives; and a process for producing the corresponding xcex2-aminoepoxide derivatives by treating the xcex2-aminoalcohol derivatives with a base.
Optically active a-aminohalomethyl ketones are known to be important compounds as an intermediate for the synthesis of an HIV protease inhibitor or the like (Refer to, for example, D. P. Getman, et al., Journal of Medicinal Chemistry, 36, 288(1993); Y. Okada, et al., Chemical and Pharmaceutical Bulletin, 36, 4794(1988); European Patent EP 346867; P. Raddatz, et al., Journal of Medicinal Chemistry, 34, 3267(1991)). There are accordingly demands for the development of a process for producing xcex1-aminohalomethyl ketones which is economical and efficient, and is therefore suited for industrial production.
An object of the present invention is to provide a process for producing xcex1-aminohalomethyl ketones and compounds related thereto which process is economical and efficient and is therefore suited for industrial production.
With a view to attaining the above-described object, the present inventors have carried out an extensive investigation. As a result, it has been found that catalytic reduction of an xcex1-aminodihalomethyl ketone derivative readily yields the intended xcex1-aminohalomethyl ketone derivative. Based on such a finding, the present invention has been completed.
Accordingly, the present invention relates to a process for producing the xcex1-aminohalomethyl ketone derivative represented by the general Formula (2) below which comprises subjecting the corresponding xcex1-aminodihalomethyl ketone derivative represented by the general Formula (1) below to catalytic reduction; a process for producing the xcex2-aminoalcohol derivative which comprises reducing such an xcex1-aminohalomethyl ketone derivative; and a process for producing the xcex2-aminoepoxide derivative which comprises treating such a xcex2-aminoalcohol with a base. 
wherein, B1 and B2 represent, each independently, a hydrogen atom or an amino-protecting group, or B1 and B2 are coupled together to represent an imino type protecting group (with the proviso that B1 and B2 do not represent a hydrogen atom at the same time), A1 represents a C1-10 alkyl group, C6-15 aryl group or C7-20 aralkyl group which groups may be optionally substituted thereon, or a group containing, in the carbon skeleton of such group, a hetero atom, and X1 represents a chlorine atom or a bromine atom. 
wherein, B3 and B4 represent, each independently, a hydrogen atom or an amino-protecting group and A1 and X1 have the same meanings as described above, respectively.
The present invention will now be described more specifically hereinafter.
In the general Formulas in the present description, A1 represents a hydrogen atom, a C1-10 alkyl group, C6-15 aryl group or C7-20 aralkyl group, these groups being able to have a substituent thereon, or a group containing, in the carbon skeleton of such group, a hetero atom. Examples of the groups containing a hetero atom in the carbon skeleton include methylthioethyl, t-butylthiomethyl, tritylthiomethyl, (p-methylbenzyl)thiomethyl, (p-methoxybenzyl)thiomethyl, t-butoxymethyl, benzyloxymethyl, t-butoxyethyl, benzyloxyethyl, 4-(t-butoxy)phenylmethyl, 4-benzyloxyphenylmethyl, phenylthiomethyl and the like groups. When the above-exemplified groups have one or more substituents, there are imposed no particular limitations on the substituent(s) insofar as it does or they do not adversely affect the reaction of the present invention. Examples thereof include alkoxyl groups, nitro group, alkyl groups, halogen atoms and the like.
Such a group can be introduced, for example, using an amino acid as a starting material. When A1 represents, e.g., a hydrogen atom, a methyl group, an isopropyl group, a 2-methylpropyl group, a 1-methylpropyl group, a benzyl group and a methylthioethyl group, such groups can be introduced by using, as a starting material, glycine, alanine, valine, leucine, isoleucine, phenylalanine and methionine, respectively.
Alternatively, A1 may be a group introduced by using, as a starting material, an amino acid which has a functional group protected on the side chain of the amino acid. Examples of such amino acid include S-t-butylcysteine, S-tritylcysteine, S-(p-methylbenzyl)cysteine, S-(p-methoxybenzyl)cysteine, O-t-butylserine, O-benzylserine, O-t-butylthreonine, O-benzylthreonine, O-t-butyltyrosine and O-benzyltyrosine.
A1 is not limited to a group introduced from a starting material derived from a natural amino acid, but may be a group introduced from a starting material derived from a non-natural amino acid (for example, a cyclohexylmethyl group, a phenyl group, a phenylthiomethyl group, or the like).
In the general Formulas given in the present description, X1 represents a chlorine atom or a bromine atom.
In the general Formulas given in the present description, B1 and B2 represent, each independently, a hydrogen atom or an amino-protecting group, or B1 and B2 are coupled together to represent an imino type protecting group. B1 and B2, however, do not represent a hydrogen atom at the same time.
There are no particular limitations imposed on the amino-protecting groups. For example, amino-protecting groups as described in xe2x80x9cProtecting Groups in Organic Chemistry, 2nd editionxe2x80x9d (John Wiley and Sons, Inc. 1991) or the like can be employed. Examples thereof include carbamate type protecting groups such as methoxycarbonyl, ethoxycarbonyl, t-butoxycarbonyl, benzyloxycarbonyl, fluorenylmethoxycarbonyl and the like; acyl type protecting groups such as acetyl, benzoyl and the like; sulfonyl type protecting groups such as methanesulfonyl, benzenesulfonyl, p-toluenesulfonyl and the like; alkyl type protecting groups such as benzyl, p-methoxybenzyl and the like; dialkyl type protecting groups such as dibenzyl and the like; silyl type protecting groups such as trimethylsilyl and the like; and imine type protecting groups such as diphenylmethylene, phenylmethylene, p-methoxyphenylmethylene and the like. Among them, the carbamate type protecting groups are preferred because they can be eliminated easily.
When B1 and B2 are coupled together to represent an imino type protecting group, the xcex1-aminodihalomethyl ketone derivative of the general Formula (1) can, in turn, be represented by the following general Formula (9): 
wherein, R2 and R3 represent, each independently, an aryl group or lower alkyl group which groups may be optionally substituted, or a hydrogen atom. Alternatively, R2 and R3 may be coupled together directly or via a proper group to represent a cyclic structure.
In the general Formulas given in the present description, B3 and B4 represent, each independently, a hydrogen atom or an amino-protecting group. Examples of the amino-protecting group can be the same as those exemplified above.
The xcex1-aminodihalomethyl ketone derivatives represented by the general Formula (1) can be prepared by reacting, as illustrated in the below-described scheme, an xcex1-amino acid ester derivative of the general Formula (10) with a dihalomethyl lithium represented by the general Formula (11). As the dihalomethyl lithium of the general Formula (11), dichloromethyl lithium or dibromomethyl lithium can be used. 
wherein, B9 and B10 represent, each independently, a hydrogen atom or an amino-protecting group, or B9 and B10 may be coupled together to represent an imino type protecting group with the proviso that B9 and B10 do not represent a hydrogen atom at the same time. As the amino-protecting group, those exemplified above can be employed.
In the general Formula (10), R4 represents a lower alkyl or aralkyl group which groups may be optionally substituted. Examples of such lower alkyl or aralkyl group which groups may be optionally substituted include straight- or branched-chain, saturated C1-8 alkyl groups which may be optionally substituted and C7-15 aralkyl groups which may be optionally substituted. Among them, particularly preferred are straight- or branched-chain, saturated C1-3 alkyl groups, such as methyl, ethyl, propyl, isopropyl and a benzyl group which may be optionally substituted. When such groups have one or more substituents, no particular limitations are imposed on the substituent insofar as it does or they do not adversely affect the reaction of the present invention. Examples thereof include alkoxyl groups, nitro group, alkyl groups, halogen atoms and the like.
The xcex1-amino acid ester derivatives represented by the general Formula (10) having the amino group protected can be prepared from an xcex1-amino acid ester and a salt thereof, or an xcex1-amino acid in accordance with the conventional manner.
An N-carbamate-protected xcex1-amino acid ester which is particularly preferred as the xcex1-amino acid ester derivative according to the present invention can be easily synthesized from an xcex1-amino acid ester and a salt thereof by the method ordinarily employed for peptide synthesis.
Furthermore, when the xcex1-amino acid dihalomethyl ketone derivatives of the general Formula (1) above are in the form of those which are protected with an imino group as represented by the general Formula (9), it can be prepared by reacting an xcex1-amino ester derivative of the general Formula (15) with a methyl halolithium, as has been described above. The xcex1-amino acid ester derivatives represented by the general Formula (15) can easily be prepared, as shown in the below-described scheme, from an xcex1-amino acid ester of the general Formula (12) or a salt thereof and an imine compound of the general Formula (13) or an aldehyde or ketone compound of the general Formula (14) in accordance with the known method (for example, A. Dondoni, et al., Synthesis, 1162(1993), M. J. O""Donnell, et al., Journal of Organic Chemistry, 47, 2663(1982)). 
wherein, R1, R2, R3 and A1 have each the same meaning as described above, respectively.
Next will be given the description of a process for preparing the xcex1-aminodihalomethyl ketone derivatives of the general Formula (1) above by reacting an xcex1-amino acid ester derivative of the general Formula (10) above, with a dihalomethyl lithium of the general Formula (11) above.
The dihalomethyl lithium of the general Formula (11) can be prepared, as shown in the below-described scheme, from a dihalomethane of the general Formula (16) and a lithium amide of the general Formula (17). 
wherein, X1 has the same meaning as described above, and R5 and R6 represent, each independently, an alkyl or trialkylsilyl group, or R5 and R6 may be coupled together directly or via a proper group to represent a cyclic structure.
Examples of the alkyl group include methyl, ethyl, isopropyl, cyclohexyl groups and the like, while those of the trialkylsilyl group include trimethylsilyl and the like. When R5 and R6 are coupled together to represent a cyclic structure, that structure represented by the general Formula (18) can be mentioned as an example. 
As the dihalomethane of the general Formula (16) given above, dichloromethane or dibromomethane is usable. Examples of the lithium amide of the general Formula (17) given above include lithium dimethylamide, lithium diethylamide, lithium diisopropylamide, lithium dicyclohexylamide, lithium 2,2,6,6-tetramethylpiperidide, lithium bis(trimethylsilyl)amide, and the like. Among them, particularly preferred is lithium diisopropylamide.
Among dihalomethyl lithiums, dichloromethyl lithium can also be prepared in accordance with the below-described scheme from dichloromethane and a lower alkyl lithium of the general Formula (19) below. 
wherein, R7 represents a lower alkyl group.
Examples of the lower alkyl group include straight- or branched-chain, saturated C1-8 alkyl groups, with straight-chain, saturated C4-6 alkyl groups such as n-butyl, n-pentyl, n-hexyl groups and the like being particularly preferred.
The xcex1-amino acid ester derivative can be reacted with the dihalomethyl lithium, for example, by either one of the following two procedures.
1) A dihalomethyl lithium is prepared in advance by reacting a lithium amide or a lower alkyl lithium with a dihalomethane. To the resultant reaction mixture is then added an xcex1-amino acid ester derivative. The reaction is preferably effected at a temperature ranging from about xe2x88x92120xc2x0 C. to xe2x88x9250xc2x0 C.
2) In the presence of an amino acid ester derivative, lithium amide or a lower alkyl lithium is allowed to act on a dihalomethane, whereby the corresponding dihalomethyl lithium is formed in the reaction system. The reaction temperature preferably ranges from about xe2x88x92120xc2x0 C. to 10xc2x0 C. Reaction can be effected at a relatively high temperature, for example, xe2x88x9220xc2x0 C. When the reaction is conducted in this procedure, a carbamate group is preferred as an amino-protecting group.
Preferred examples of the reaction solvent include ether solvents such as tetrahydrofuran, diethyl ether, t-butylmethyl ether and the like. In some cases, such a solvent may be mixed with a nonpolar solvent such as toluene, hexane or the like. This reaction proceeds promptly at a temperature ranging from about xe2x88x92120xc2x0 C. to 10xc2x0 C. The reaction is usually completed at xe2x88x9280xc2x0 C. to xe2x88x9220xc2x0 C. in 5 to 60 minutes. After completion of the reaction, the reaction mixture may be treated with an aqueous solution of ammonium chloride, a phosphate buffer, dilute hydrochloric acid, dilute sulfuric acid, an aqueous solution of potassium hydrogensulfate or the like.
The xcex1-aminodihalomethyl ketone derivative thus obtained can be purified by procedures known per se in the art such as recrystallization, column chromatography or the like. If there are caused no adverse effects, the derivative may be provided for the subsequent reaction without separation or purification.
The xcex1-aminodihalomethyl ketone derivative (of the general Formula (1)) can be changed into the xcex1-aminohalomethyl ketone derivative (of the general Formula (2)) by a catalytic reduction. Catalytic reduction can be conducted in a manner known per se in the art. There are no particular limitations imposed on the catalysts to be used for reduction insofar as they allow the reaction to proceed smoothly. Examples thereof include palladium, rhodium, ruthenium, platinum, nickel and the like. These catalysts may be held on carbon or the like or may contain water. Among them, palladium is preferred, and it is usually used in the form where it is held on activated charcoal, silica, alumina, barium sulfate, calcium carbonate or the like. Preferred specific examples thereof include palladium-carbon, Lindlar""s catalyst (palladium/barium sulfate) and the like. For the catalytic reduction of the xcex1-aminodibromomethyl ketone according the present invention, use of a Lindlar""s catalyst is preferred. No particular limitations are imposed on the amount of the catalyst to be used, insofar as it permits completion of the intended reaction. Usually, the catalyst is used in an amount of 0.01 to 10 mole %, preferably 0.1 to 5 mole % relative to the mole number of the xcex1-dihalomethylketone derivative.
As a solvent to be used for reduction, no particular limitations are imposed thereon insofar as it does not adversely affect the reaction and at the same time, permits dissolution of starting materials therein to an extent necessary for the reaction. Examples thereof include water, methanol, ethanol, ethyl acetate and tetrahydrofuran, and a mixture solvent of two or more thereof. To such a solvent, a base such as triethylamine or the like may be added as needed. For example, when a Lindlar""s catalyst is employed as the catalyst, it is recommended to neutralize the hydrogen halide byproduced upon reaction with the use of base such as triethylamine. No particular limitations are imposed on the amount of the solvent to be used, insofar as it does not disturb efficient stirring of the reaction mixture. The solvent is usually used in an amount of 1 to 100 times the volume, preferably 5 to 25 times the volume relative to the weight of the xcex1-aminodihalomethyl ketone derivative.
There are no particular limitations imposed on the hydrogen pressure upon reduction, insofar as it permits smooth progress of the reaction. It is preferably 1 to 10 atmospheric pressure.
Concerning the reaction temperature, no particular limitations are imposed thereon, insofar as it permits progress of the resultant reaction and does not permit decomposition of the resultant reaction product. It is usually 0 to 120xc2x0 C., preferably 20 to 60xc2x0 C.
After completion of the reaction, the catalyst may be filtered off, and the solvent may be distilled off. The hydrogen halide byproduced upon catalytic reduction can be removed from the reaction system or mixture by adding thereto an amine such as triethylamine, diisopropylethylamine or the like during or after the catalytic reduction whereby the hydrogen halide is converted into the corresponding amine salt, solidifying the resulting amine salt with the use of, or in, a proper solvent such as ethyl acetate, t-butylmethyl ether, toluene and the like, and then filtering off the resulting solid from the reaction system.
The xcex1-aminohalomethyl ketone derivative thus obtained can be purified in a manner known per se in the art such as recrystallization, column chromatography or the like. It may be provided for the subsequent reaction without separation and purification, if there are caused no adverse effects.
With regard to the catalytic reduction step employed in the present invention, a preparation example of an xcex1,xcex1-dialkyl-xcex1-aminochloromethyl ketone by catalytic reduction of an xcex1,xcex1-dialkyl-xcex1-aminodichloromethyl ketone in the racemic form is disclosed in Japanese Patent Application Laid-open (Kokai) No. Hei 10-316563 and Japanese Patent Application Laid-Open (Kokai) No. Hei 10-95757. An actual example of catalytic reduction of an xcex1-monoalkyl-xcex1-aminodichloromethyl ketone is, however, not disclosed anywhere therein.
Furthermore, there have been no reports on the use of an optically active substance, so it has been utterly unknown whether optical activity can be retained or not upon catalytic reduction according to the present invention. Moreover, there have been utterly no reports on a preparation example of xcex1-aminobromomethyl ketone by catalytic reduction of xcex1-aminodibromomethyl ketone.
The compounds according to the present invention include mixtures at any ratio of the two optically active substances including the racemic form, and the two optically active substances. The production process of the present invention can be applied to the synthesis of a compound having optical activity (i.e., an optically active compound) by using an optically active xcex1-amino acid ester obtainable from the esterification of the corresponding optically active amino acid. Optically active amino acids are medically important. I.e., as an xcex1-amino acid ester to be employed as the raw material, that in the L form or D form is preferred, with L-phenylalanine ester useful as the starting material for an HIV protease inhibitor being particularly preferred.
According to the present invention, when an optically active xcex1-amino acid ester derivative is used as the xcex1-amino acid ester derivative, a raw material, the corresponding optical activity can be maintained in the xcex1-aminohalomethyl ketone derivative of the general Formula (2) obtainable by the production process of the present invention. Accordingly, the production process of the present invention is markedly useful as a synthesis process of intermediate compounds for pharmaceuticals.
The following is the reaction scheme when one of the two optically active substances is employed according to the present invention. 
wherein, * represents an asymmetric carbon atom, and B1, B2, B3, B4, A1 and X1 have the same meanings as described above, respectively.
Additionally, a production example of an xcex1-aminohalomethyl ketone derivative (S form according to in the R/S convention) useful as an intermediate for an HIV protease inhibitor derived from L-phenylalanine is shown below. 
wherein, R1 represents a lower alkyl group, benzyl group or fluorenylmethyl group, and X1 has the same meaning as described above.
Examples of the lower alkyl group include straight- or branched-chain, saturated C1-8 alkyl groups, out of which the methyl, ethyl and t-butyl groups are preferred.
It is known that the xcex1-aminohalomethyl ketone derivative represented by the general Formula (1) can be changed into the corresponding, but more advanced intermediate through, e.g., the existing two-stage reaction step as shown below (Refer to D. P. Getman, et al., Journal of Medicinal Chemistry, 36, 288(1993)).
Described specifically, the xcex1-aminohalomethyl ketone derivative represented by the general Formula (2) can be changed, by the reduction of the carbonyl group thereof, into the corresponding xcex2-amino alcohol derivative represented by the general Formula (7), and the resulting derivative can be readily epoxidated under alkaline conditions, whereby a xcex2-aminoepoxide derivative represented by the general Formula (8) can be obtained. 
In the Formula (7), B5 and B6 represent, each independently, a hydrogen atom or an amino-protecting group, and A1 and X1 have the same meanings as described above, while in the Formula (8), B7 and B8 represent, each independently, a hydrogen atom or an amino-protecting group, and A1 and X1 have the same meanings as described above.
The production process of the present invention includes, in addition to the case where the protecting group is maintained or not eliminated, the case where after deprotection, reprotection is carried out with the use of the same or another protecting group, the case where after deprotection, re-protection is not conducted, and the case where a protecting group is converted into another protecting group by reaction.